Generator Grounding

[Jennie1220]

I had a question about generator grounding. Typically, when we install generators we use a 4 pole ATS that switches the neutral so the generator is considered a separately derived. In this system the ground and neutral are bonded together at the generator and the generator has its own ground rod.

The job I am working on now is a little different because the ATS is only a 3 pole so it does not switch the neutral. As a result the generator is considered a non separately derived system. In this system the bonding jumper between the neutral and the ground is removed and according to 250.35(B) a bonding jumper needs to be installed between the generator equipment grounding terminal and the equipment grounding terminal in the generator control panel (disconnecting means). And no ground rod is needed. Is this correct?

 

[augie47]

That is correct. Neutral and equipment grounding must remain separate per 250.24 (A)(5)
(some manufacturers call for a ground rod to be connected to the frame but that's not a Code requirement)

 

[ron]

Many times when we have a 3 pole transfer, we bond the N-G at the gen and utility service disconnect and do NOT bring a neutral downstream of that equipment (because the downstream equipment on many o9f my designs do not need a neutral - 480V). When we need a neutral downstream, we put in a small 480-480/277V transformer to derive the neutral for the loads they are needed.
That way we don't have to worry about the extra copper or neutral transfers.